At present a routine method for preparing fuel-air mixture consists in producing a hydrogen-containing gas from fuel and feeding said gas in the fuel-air mixture.
One prior-art method for preparing fuel-air mixture for an internal combustion engine is known to effect in three stages, that is, at the first stage the fuel is partially decomposed by virtue of the heat of exhaust gases, at the second stage the fuel is preheated by said gases, and at the third stage catalytic fuel decomposition occurs. To promote catalytic fuel decomposition at said stage the fuel is additionally preheated by exhaust gases (U.S. Pat. No. 4,147,142).
However, the use of only the heat of exhaust gases for fuel decomposition is inadequate to attain an efficient and stable running of the fuel decomposition process.
One more state-of-the-art method for preparing fuel-air mixture for an internal combustion engine is known to consist in splitting the mixture into two flows, that is, a greater main flow and a smaller auxiliary flow, separating part of the mixture from the auxiliary flow, and burning the latter in order to heat and evaporate the remainder part of the auxiliary flow by the resultant gases, followed by mixing both parts of the auxiliary flow and feeding an integrated flow to the catalytic chamber. Before being fed to the combustion chamber the preconditioned auxiliary flow of the mixture is intermixed with the main flow of the fuel-air mixture (U.S. Pat. No. 3,901,197).
Use of an open fire, according to the known method, for burning part of the fuel from the fuel-air mixture adds to the efficiency of thermal fuel decomposition, however, it increases fuel consumption and is hazardous. A danger of flame travel and an outbreak of fire arises when an engine runs unsteadily or misses, as the velocity of flame travel in the fuel-air mixture may exceed the flow velocity of the mixture itself.
Moreover, unburnt hydrocarbons of the C.sub.n H.sub.n+2 type are left after burning an enriched mixture, which are deposited in the catalyst pores as soot and coke, thus putting the catalyst out of order.
As is evident from specification of the heretofore-known methods for decomposition of liquid fuel, said methods involve use of catalysts which are not only expensive components of the fuel-air preparation device but also require periodical replacement, inasmuch as anti-knocking dopes present in the fuel are detrimental to catalysts.
Still one more prior-art method for preparing fuel-air mixture for internal combustion engines is known to be the nearest in spirit to the herein-proposed method and consists in that two flows of fuel-air mixture are established. One of the two flows is overenriched below the ignition range and heated to a temperature of 400.degree.-800.degree. C. with exhaust gases having a temperature of about 750.degree. C. to obtain carbon monoxide and hydrogen-containing gases and mixed with the other flow before being fed to the engine cylinder (DE A1 3,607,007).
However, the fuel decomposition process is known commonly to proceed most efficaciously at a temperature about 850.degree. C. which cannot be reached by the method in question.
Known in the present state of the art are devices for carrying into effect the methods for preparing fuel-air mixture for internal combustion engines, comprising as a rule heat-exchangers for preheating fuel-air mixture by the heat of exhaust gases, and reactors with a catalyst.
To provide more efficient process for decomposition of the fuel molecules use is made of an additional heating arrangement of fuel-air mixture to a higher temperature than that of exhaust gases.
One prior-art device for preparing fuel-air mixture is known to comprise an additional heating arrangement with an ignition spark and a burner to which the fuel-air mixture is fed and burns therein in an open fire, after which said mixture is fed to the reactor with a catalyst, wherein part of the liquid fuel molecules get decomposed (DE B2, 2,613,348).
One more prior-art device for preparing the fuel-air mixture for internal combustion engines is known to comprise a reactor situated in the exhaust manifold close to the exhaust valves and shaped as a blind-end (at the side facing said exhaust valves) pipe running axially and centrally of the exhaust pipe. Fuel, water, and air are fed, in a stringently fixed ratio, to the reactor nearby its blind-end. In its alternative version, the known device comprises a heat-exchanger located also in the exhaust pipe past the reactor as along the direction of flow of the engine exhaust gases (DE A1 3,607,007).
Low efficiency of the processes proceeding in the known device has been discussed above.
It is common knowledge that high temperatures of exhaust gases occur only at the first instant of the exhaust stroke, then their temperature drops abruptly. Taking into account the transient nature of the exhaust process (which equals one-fourth of a crankshaft revolution per two complete revolutions thereof), as well as of the fact that the temperature of a heat-transfer agent used for preconditioning the fuel-air mixture without its preheating is as low as 750.degree. C. compared to 900.degree. C. with preheating. One cannot expect a stable process of decomposition of the liquid fuel molecules.
Furthermore, having impinged upon the front reactor wall at the hottest spot thereof, the fuel particles thereafter might not collide with said wall or might come in contact with colder reactor areas, that is, only a once-through process of decomposition of the fuel molecules is possible, which is quite ineffective. On the other hand, provision of a special pump for feeding the fuel-air mixture to the reactor adds to the cost of the device as a whole, whereas the higher temperature of exhaust gases involves increased fuel consumption.
A device for preconditioning the fuel-air mixture for internal combustion engines that is nearest in spirit to that herein-proposed, comprises a double-loop heat-exchanger having an inlet and an outlet piping, a proportioner of the components of the mixture being treated, and an igniter provided at the outlet of the first loop of the heat-exchanger before the catalyst-containing chamber. The input and output pipings of the second loop of the heat-exchanger are connected respectively to the engine exhaust pipe and to the surrounding atmosphere, and the mixing nozzle of the proportioner is connected to the first heat-exchanger loop through a controlled member (SU A1 493,073).
As is evident from the above discussion of the heretofore-known devices, use is therein made of catalysts on a platinum support which renders said devices too expensive, whereas use of a heat-transfer agent hotter than the engine exhaust gases makes the device in question uneconomical, too.